1. Field of the Invention
This invention relates to a method of separating a semiconductor thin film deposited on a porous layer, a process for producing a semiconductor member, a process for producing a solar cell formed of a thin-film single crystal layered on a low-cost substrate, and an anodizing apparatus used in these.
2. Related Background Art
A technique is known in which a thin-film semiconductor layer is formed on a porous layer formed at the surface portion or layer of a semiconductor substrate and thereafter the semiconductor layer is separated at the part of the porous layer. As a separation method, used is a chemical method making use of etching or a physical method of causing ultrasonic waves or force such as tensile force to act on.
With regard to the physical method, Japanese Patent Application Laid-Open No. 7-302889 discloses that a porous layer is formed at the surface of a silicon wafer, thereafter an epitaxial growth layer is formed thereon, another wafer is bonded to the epitaxial growth layer (silicon layer), and a pressure, a shear force or ultrasonic waves is/are applied to the porous layer to make separation. Japanese Patent Application Laid-Open No. 8-213645 also discloses that a porous layer is formed at the surface of a single-crystal silicon substrate, thereafter a p-n junction layer is formed thereon, the single-crystal silicon substrate is, on its back, fastened to a jig through an adhesive, another jig is bonded to the epitaxial growth layer, and both the jigs are pulled against each other to cause the porous layer to break to obtain a thin-film epitaxial growth layer (a solar cell). Japanese Patent Application Laid-Open No. 10-190032 discloses that a difference in shrink between a silicon layer and a plastic substrate bonded to the silicon layer is utilized to separate the former from the latter by cooling them with a vapor of liquid nitrogen.
However, when the thin-film epitaxial growth layer is obtained by separating it at the part of the porous layer, the thin-film semiconductor layer may finely be cracked or broken on the periphery of a region where it is to be separated (i.e., a separating region), because of an impact produced when the porous layer formed at the surface of the first substrate is broken by separating force. Where it is thus cracked or broken, not only the thin film can be handled with difficulty but also, when cracked or broken up to the central area, the yield and characteristics of devices including solar cells may lower.
An object of the present invention is to provide a process for producing a semiconductor member and a solar cell, which process enables separation of the thin-film semiconductor layer at a small force while causing less cracks, breaks or defects to be brought into it and can manufacture high-performance semiconductor members and solar cells in a good efficiency.
To achieve the above object, the present invention provides a process for producing a semiconductor member making use of a thin-film crystal semiconductor layer, the process comprising the steps of:
(1) anodizing the surface of a first substrate to form a porous layer at least on one side of the substrate;
(2) forming a semiconductor layer at least on the surface of the porous layer;
(3) removing the semiconductor layer at its peripheral region;
(4) bonding a second substrate to the surface of the semiconductor layer;
(5) separating the semiconductor layer from the first substrate at the part of the porous layer by applying an external force to at least one of the first substrate, the porous layer and the second substrate; and
(6) treating the surface of the first substrate after separation and repeating the above steps (1) to (5).
The present invention also provides a process for producing a semiconductor member making use of a thin-film crystal semiconductor layer, the process comprising the steps of:
(1) anodizing the surface of a first substrate to form a porous layer at least on one side of the substrate;
(2) forming a semiconductor layer at least on the surface of the porous layer;
(3) bonding a second substrate to the semiconductor layer;
(4) removing the semiconductor layer at its region not covered with the second substrate;
(5) separating the semiconductor layer from the first substrate at the part of the porous layer by applying an external force to at least one of the first substrate, the porous layer and the second substrate; and
(6) treating the surface of the first substrate after separation and repeating the above steps (1) to (5).
The present invention still also provides a process for producing a solar cell making use of a thin-film crystal semiconductor layer, the process comprising the steps of:
(1) anodizing the surface of a first substrate to form a porous layer at least on one side of the substrate;
(2) forming a semiconductor layer at least on the surface of the porous layer;
(3) removing the semiconductor layer at its peripheral region;
(4) bonding a second substrate to the surface of the semiconductor layer;
(5) separating the semiconductor layer from the first substrate at the part of the porous layer by applying an external force to at least one of the first substrate, the porous layer and the second substrate; and
(6) treating the surface of the first substrate after separation and repeating the above steps (1) to (5).
The present invention further provides a process for producing a solar cell making use of a thin-film crystal semiconductor layer, the process comprising the steps of:
(1) anodizing the surface of a first substrate to form a porous layer at least on one side of the substrate;
(2) forming a semiconductor layer at least on the surface of the porous layer;
(3) bonding a second substrate to the semiconductor layer;
(4) removing the semiconductor layer at its region not covered with the second substrate;
(5) separating the semiconductor layer from the first substrate at the part of the porous layer by applying an external force to at least one of the first substrate, the porous layer and the second substrate; and
(6) treating the surface of the first substrate after separation and repeating the above steps (1) to (5).
The present invention still further provides a process for producing a semiconductor member obtained by separating a thin-film crystal semiconductor layer formed on a first substrate to transfer the former to a second substrate, wherein the thin-film crystal semiconductor layer is removed by etching by electropolishing at its part on the periphery of the first substrate.
The present invention still further provides a process for producing a semiconductor member making use of a thin-film crystal semiconductor layer, the process comprising the steps of:
(1) anodizing the surface of a first substrate at least on its principal-surface side to form a porous layer;
(2) forming a semiconductor layer on the surface of the porous layer;
(3) removing the semiconductor layer at its part on the periphery of the first substrate by electropolishing;
(4) bonding a second substrate to the surface of the semiconductor layer;
(5) separating the semiconductor layer from the first substrate at the part of the porous layer to transfer the semiconductor layer to the second substrate; and
(6) treating the surface of the first substrate after separation and repeating the above steps (1) to (5).
The above process may further comprise, between the steps (5) and (6), the step of forming a semiconductor junction on the surface of the semiconductor layer having been transferred to the second substrate.
The second substrate may comprise a flexible film, and force that acts in the direction where the film is separated from the first substrate may be applied to separate the semiconductor layer at the part of the porous layer. The flexible film may comprise a resinous film.
The present invention still further provides a process for producing a solar cell obtained by separating a thin-film crystal semiconductor layer formed on a first substrate to transfer the former to a second substrate, wherein the thin-film crystal semiconductor layer is removed by etching by electropolishing at its part on the periphery of the first substrate.
The present invention still further provides a process for producing a solar cell making use of a thin-film crystal semiconductor layer, the process comprising the steps of:
(1) anodizing the surface of a first substrate at least on its principal-surface side to form a porous layer;
(2) forming a semiconductor layer on the surface of the porous layer;
(3) removing the semiconductor layer and the porous layer at their part on the periphery of the first substrate by electropolishing;
(4) forming a surface anti-reflection layer on the surface of the semiconductor layer at its part other than that on the periphery of the first substrate;
(5) bonding a second substrate to the surface of the semiconductor layer;
(6) separating the semiconductor layer from the first substrate at the part of the porous layer to transfer the semiconductor layer to the second substrate; and
(7) treating the surface of the first substrate after separation and repeating the above steps (1) to (6).
The above process may further comprise, between the steps (6) and (7), the step of forming a semiconductor junction on the surface of the semiconductor layer having been transferred to the second substrate.
The second substrate may comprise a flexible film, and force that acts in the direction where the film is separated from the first substrate may be applied to separate the semiconductor layer at the part of the porous layer. The flexible film may comprise a resinous film.
The present invention still further provides an anodizing apparatus comprising, at the peripheral portion of a substrate to be subjected to anodizing, a first electrode coming in contact with the back side of the substrate and a second electrode facing the first electrode, interposing the substrate between them; the first electrode having substantially the same form as the second electrode.
The present invention still further provides an anodizing apparatus comprising, at the peripheral portion of a substrate to be subjected to anodizing, a first electrode coming in contact with the back side of the substrate and a second electrode facing the first electrode, interposing the substrate between them, and, in the remaining substrate region excluding the peripheral portion, a third electrode coming in contact with the back side of the substrate and a fourth electrode facing the third electrode, interposing the substrate between them; the first electrode and third electrode having substantially the same form as the second electrode and fourth electrode, respectively.